Method and apparatus to reduce the impact of raman interference in passive optical networks with RF video overlay
Raman interference (also known as Raman scattering) during an idle frame transmission state in a passive optical network (PON) having radio frequency video overlay is reduced by generating and transmitting data packets having both random data and random length. Randomly varying both the packet data content and the packet length can achieve significant improvement in Raman interference reduction. The random packet data and length in effect spreads the interference across a spectrum wide enough that there is no interference effect perceptible to a television viewer.
1. A method for reducing interference in a passive optical network
(PON) having radio frequency video overlay during an idle frame transmission state, the method comprising:
detecting an idle frame transmission state in response to a signal indicating that packet data is not available:
generating a first random number as a random length for an idle pattern and generating a second random number as random data of the idle pattern;
generating frames having headers comprising the first random length while idle frame transmission state is detected,
generating frames having headers with destination addresses not associated with any optical network terminal of the PON while the idle frame transmission state is detected;
generating frames for transmission on the PON using the idle pattern in response to the detection of the idle frame transmission state; and
generating frames for transmission on the PON having source data while the idle frame transmission state is not detected.
2. The method claimed in claim 1 , wherein:
the step of generating frames for transmission on the PON using the random length, random data idle pattern conforms to the GPON encapsulation method (GEM) standard; and
the step of generating frames for transmission on the PON having source data conforms to the GPON encapsulation method (GEM) standard.
3. A system for reducing interference in a passive optical network (PON) having radio frequency video overlay during an idle frame transmission state, the system comprising: a pseudo-random pattern generator for generating as separate outputs a First random number and a second random number;
generator logic for utilizing the first random number to determine a length of an idle pattern and utilizing the second random number as random data of the idle pattern;
header generator logic for generating frames having headers comprising the first random length while the idle frame transmission state is detected, and generating frames having headers with destination addresses not addressed to any optical network terminal of the PON while the idle frame transmission state is detected: and
control logic for recognizing an idle frame transmission state upon receipt of a signal that packet data is not available and enabling generation of frames for transmission on the PON having source data while the idle frame transmission state is not detected and
enabling generation of frames for transmission on the PON using the identified idle pattern in response to the detection of the idle frame transmission state.
4. The system claimed in claim 3 , wherein the generator logic conforms to the GPON encapsulation method (GEM) standard.
5. The system claimed in claim 3 , wherein the pseudo-random number generator comprises a linear-feedback shift register.